devmapper: Add lock to protext Devices map

Currently access to the Devices map is serialized by the main
DeviceSet lock, but we need to access it outside that lock, so we
add a separate lock for this and grab that everywhere we modify
or read the map.

Docker-DCO-1.1-Signed-off-by: Alexander Larsson <alexl@redhat.com> (github: alexlarsson)

runtime/graphdriver/devmapper/deviceset.go

@@ -51,7 +51,8 @@ type DevInfo struct {
 }
 
 type MetaData struct {
-	Devices map[string]*DevInfo `json:devices`
+	Devices     map[string]*DevInfo `json:devices`
+	devicesLock sync.Mutex          `json:"-"` // Protects all read/writes to Devices map
 }
 
 type DeviceSet struct {
@@ -179,7 +180,9 @@ func (devices *DeviceSet) allocateTransactionId() uint64 {
 }
 
 func (devices *DeviceSet) saveMetadata() error {
+	devices.devicesLock.Lock()
 	jsonData, err := json.Marshal(devices.MetaData)
+	devices.devicesLock.Unlock()
 	if err != nil {
 		return fmt.Errorf("Error encoding metadata to json: %s", err)
 	}
@@ -215,6 +218,8 @@ func (devices *DeviceSet) saveMetadata() error {
 }
 
 func (devices *DeviceSet) lookupDevice(hash string) (*DevInfo, error) {
+	devices.devicesLock.Lock()
+	defer devices.devicesLock.Unlock()
 	info := devices.Devices[hash]
 	if info == nil {
 		return nil, fmt.Errorf("Unknown device %s", hash)
@@ -233,10 +238,15 @@ func (devices *DeviceSet) registerDevice(id int, hash string, size uint64) (*Dev
 		devices:       devices,
 	}
 
+	devices.devicesLock.Lock()
 	devices.Devices[hash] = info
+	devices.devicesLock.Unlock()
+
 	if err := devices.saveMetadata(); err != nil {
 		// Try to remove unused device
+		devices.devicesLock.Lock()
 		delete(devices.Devices, hash)
+		devices.devicesLock.Unlock()
 		return nil, err
 	}
 
@@ -632,10 +642,14 @@ func (devices *DeviceSet) deleteDevice(info *DevInfo) error {
 	}
 
 	devices.allocateTransactionId()
+	devices.devicesLock.Lock()
 	delete(devices.Devices, info.Hash)
+	devices.devicesLock.Unlock()
 
 	if err := devices.saveMetadata(); err != nil {
+		devices.devicesLock.Lock()
 		devices.Devices[info.Hash] = info
+		devices.devicesLock.Unlock()
 		utils.Debugf("Error saving meta data: %s\n", err)
 		return err
 	}
@@ -795,7 +809,15 @@ func (devices *DeviceSet) Shutdown() error {
 	utils.Debugf("[devmapper] Shutting down DeviceSet: %s", devices.root)
 	defer utils.Debugf("[deviceset %s] shutdown END", devices.devicePrefix)
 
+	var devs []*DevInfo
+
+	devices.devicesLock.Lock()
 	for _, info := range devices.Devices {
+		devs = append(devs, info)
+	}
+	devices.devicesLock.Unlock()
+
+	for _, info := range devs {
 		info.lock.Lock()
 		if info.mountCount > 0 {
 			// We use MNT_DETACH here in case it is still busy in some running
@@ -979,12 +1001,15 @@ func (devices *DeviceSet) List() []string {
 	devices.Lock()
 	defer devices.Unlock()
 
+	devices.devicesLock.Lock()
 	ids := make([]string, len(devices.Devices))
 	i := 0
 	for k := range devices.Devices {
 		ids[i] = k
 		i++
 	}
+	devices.devicesLock.Unlock()
+
 	return ids
 }